Paired medical lead bodies with conductive shields providing destructive interference

ABSTRACT

Medical lead bodies that are paired each include a braided conductive shield. The braided conductive shield of one lead body has a value for a physical parameter that differs from a value for the physical parameter of the second lead body. The difference in values of the physical parameter for the paired lead bodies results in a reduction in heating from exposure of the lead bodies to radiofrequency energy at electrodes associated with the lead bodies. The lead bodies may be paired by being implanted adjacently to one another. The lead bodies may be further paired by being coupled to a same distal body, such as a paddle containing the electrodes.

RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 15/910,655, filed on Mar. 2, 2018, which is a divisionalapplication of U.S. Pat. No. 9,907,956, filed on Sep. 28, 2016, which isa continuation application of U.S. Pat. No. 9,763,317, filed on Oct. 17,2014, which is a U.S. national phase filing of PCT/US2013/023637, filedon Jan. 29, 2013, which claims priority to U.S. Provisional App. No.61/635,766 filed on Apr. 19, 2012.

TECHNICAL FIELD

Embodiments relate to medical leads that have braided conductiveshields. More particularly, embodiments relate to medical lead bodieswith braided conductive shields where the medical lead bodies are pairedand where the braided conductive shields have different physicalparameter values.

BACKGROUND

Medical leads provide electrical stimulation from a medical device to atarget site within a body of a patient. The medical device is typicallyimplanted or otherwise installed on the body in an accessible area atsome distance from the target site, and the medical lead is routed tothe target site either through a percutaneous procedure or by surgicalimplantation depending upon the type and size of the medical lead beingimplanted.

An issue occurs when the patient is subjected to radiofrequency (RF)electromagnetic energy in excess of the ambient, such as when having amagnetic resonance imaging (MRI) scan. The metal filars within the leadhave current induced by the RF energy. This induced current can produceheating within the medical lead and at the electrodes which can causeharm to the patient. A shield may be included within the lead to limitthe amount of current induced on the filars and thereby reduce heatingat the electrodes.

In some cases, multiple lead bodies may be paired. For instance, themultiple lead bodies may be positioned adjacently when implanted. Oneparticular example of such positioning is for surgical leads thatutilize two lead bodies to carry stimulation signals to a distal paddle.Both lead bodies may include identical braided conductive shields tolimit the amount of heating. While the amount of heating at theelectrodes may be reduced by the presence of the identical braidedconductive shields, it may be desirable to reduce the amount of heatingby an even greater amount to allow for even greater scan power levels.

SUMMARY

Embodiments address issues such as these and others by providing pairedlead bodies with braided conductive shields having different physicalparameter values. The different physical parameter values for the pairedleads result in an increased reduction of heating at the electrodesrelative to identical braided conductive shields. The physical parametermay be one of a variety of different physical characteristics such asthe weave density, weave angle, number of braid wires, braid diameter,and/or braid wire conductivity. The lead bodies may be paired by beingaligned adjacently and in close proximity for at least a portion oftheir length, where this may be achieved through in various manners suchas by positioning during implantation and/or by bonding of the leadbodies.

Embodiments provide a medical lead that includes a first lead bodyhousing a first filar connected to a first proximal contact on the firstlead body. The first lead body has a first braided conductive shieldwith a first value for a first physical parameter. The medical leadincludes a second lead body housing a second filar connected to a secondproximal contact on the second lead body, the second lead body having asecond braided conductive shield with a second value for the firstphysical parameter that is different from the first value. The medicallead also includes a body housing a plurality of electrodes, the bodybeing coupled to the distal end of the first and second lead bodies witha first electrode of the plurality connected to the first filar and asecond electrode of the plurality connected to the second filar.

Embodiments provide a medical system that includes a first lead bodyhousing a first filar connected to a first proximal contact on the firstlead body. The first lead body has a first braided conductive shieldwith a first value of a first physical parameter, and the first leadbody has a first electrode connected to the first filar. The medicalsystem includes a second lead body housing a second filar connected to asecond proximal contact on the second lead body. The second lead bodyhas a second braided conductive shield with a second value of the firstphysical parameter that is different than the first value, and thesecond lead body has a second electrode connected to the second filar.The second lead body is positioned adjacently to the first lead body.

Embodiments provide a method of implanting a medical system thatinvolves providing a first lead body housing a first filar connected toa first proximal contact on the first lead body. The first lead body hasa first braided conductive shield with a first value of a first physicalparameter. The method further involves providing a second lead bodyhousing a second filar connected to a second proximal contact on thesecond lead body. The second lead body has a second braided conductiveshield with a second value of the first physical parameter that isdifferent than the first value. A body houses a plurality of electrodesand the body is coupled to the distal end of the first and second leadbodies with a first electrode of the plurality connected to the firstfilar and a second electrode of the plurality connected to the secondfilar. The method further involves implanting the first lead body andthe second lead body such that the second lead body is positionedimmediately adjacent to the first lead body.

Embodiments provide a method of implanting a medical system thatinvolves providing a first lead body housing a first filar connected toa first proximal contact on the first lead body. The first lead body hasa first braided conductive shield with a first value of a first physicalparameter, and the first lead body has a first electrode connected tothe first filar. The method further involves providing a second leadbody housing a second filar connected to a second proximal contact onthe second lead body. The second lead body has a second braidedconductive shield with a second value of the first physical parameterthat is different than the first value, and the second lead body has asecond electrode connected to the second filar. The method furtherinvolves implanting the first lead body and the second lead body suchthat the second lead body is positioned immediately adjacent to thefirst lead body.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a medical system environment where a medicalload includes paired lead bodies having braided conductive shields withdifferent weave densities.

FIG. 2 shows a cross-sectional side view of a medical lead body.

FIG. 3 shows one example of a medical lead having lead bodies withshields that have different numbers of wires and weave densities witheven spacing of braid wires.

FIG. 4 shows one example of a medical lead having lead bodies withshields that have different weave angles and weave densities.

FIG. 5 shows one example of a medical lead having lead bodies withshields that are constructed of braid wire materials with differentconductivities.

FIG. 6 shows one example of a medical lead having lead bodies withshields that have different numbers of wires and weave densities withuneven spacing of braid wires.

FIG. 7 shows one example of a medical lead having lead bodies withshields that have different numbers of wires and weave angles.

FIG. 8 shows one example of a medical lead having lead bodies withshields that have different numbers of wires where one lead body has anasymmetric wire count and that have different weave densities.

FIG. 9 shows one example of a medical lead having lead bodies withshields that have different numbers of wires where one lead body has anasymmetric wire count and that have different weave densities withuneven spacing of braid wires.

FIG. 10 shows one example of a medical lead having lead bodies withshields that have different diameters and weave angles.

DETAILED DESCRIPTION

Embodiments provide paired medical lead bodies that have braidedconductive shields with different physical parameter values. Thisdifference in the braided conductive shields results in reduced heatingat the electrodes associated with the paired medical lead bodies. Themedical lead bodies may be paired by extending to a same paddle attachedto the distal ends of both lead bodies. The medical lead bodies may alsobe paired by being positioned during implantation immediately adjacentto one another without the distal ends necessarily being connected to asame paddle.

The pairing of the lead bodies may also be accomplished by creating abond between the lead bodies such as by gluing or melting the leadbodies together or by surrounding both lead bodies with tubing such as aheat shrink layer or an additional outer jacket. Such bonding providesthe advantages of not requiring the surgeon to properly position thelead bodies to create the pairing and also by improving thepredictability of the performance of the pairing.

FIG. 1 shows one example of a medical system 100 that is implantedwithin a body 112 of a patient. The medical system 100 includes astimulation device 102 that produces stimulation signals. First andsecond lead bodies 104, 106 have proximal ends that are coupled to thestimulation device 102. Distal ends of the first and second lead bodies104, 106 are coupled to a paddle 108 which includes electrodes thatdeliver the stimulation signals to the body 112.

In this particular example, the first and second lead bodies 104, 106are implanted such that they remain immediately adjacent to one anotherfrom proximal to distal ends. This adjacency allows the braidedconductive shields of the first and second lead bodies 104, 106 toelectrically couple in the presence of substantial levels of RF energyas might be encountered during an MRI scan. Such an RF coupling of theeshields from the adjacency of the lead bodies 104, 106 combined with thephysical parameter value differences present between the braidedconductive shields reduces the amount of heating that occurs at theelectrodes of the paddle 108 during exposure to the RF energy. Withoutbeing bound by any particular theory, it is believed that the couplingof the shields where the shields have physical parameter valuedifferences results in destructive interference of the RF waves presenton the shields.

In this example, a strain relief loop 110 is also formed by the leadbodies 104, 106. The loop 110 provides slack to reduce strain on thelead bodies 104, 106 during bodily movements by the patient. As shown,the lead bodies 104, 106 maintain their adjacent relationship within theloop 110 and thus retain the RF coupling from the proximal to distalends that reduces the electrode heating.

FIG. 2 shows a cross-sectional side view of the paddle 108 and lead body104 from the medical system 100 of FIG. 1. The paddle 108 is former by abody 202 that houses a collection of electrodes 204. The body 202 may beconstructed in the conventional manner and from conventional paddlematerials such as silicone or polyurethane.

The lead body 104 includes a jacket body 206 that extends from theproximal to distal ends. The jacket body 206 provides structural supportwhile protecting the braided shield and conductors from externalconditions. The jacket body 206 may be constructed of materials such assilicone or polyurethane.

Shield wires 208 are embedded within the jacket body 206. These shieldwires 208 form a braid that ultimately shields conductive filars 210from the RF energy to reduce the amount of current induced on the filars210. The shield wires 208 may be constructed of various biocompatibleconductors such as tantalum, titanium, MP35N, platinum, niobium, and thelike.

The filars 210 are housed by the tubular body 206 and are surrounded bythe shield wires 208. While the filars 210 are shown in a coiledconfiguration in this cross-sectional view, they may be in otherconfigurations as well such as linear cables. The coiled filars 210 areelectrically connected via a jumper portion 216 to contacts 214 that arepositioned on a proximal end of the lead body 104. The coiled filars 210are electrically connected via a jumper portion 212 to the electrodes204 within the body 202 of the paddle 108. The filars may be constructedof biocompatible conductors such as MP35N, titanium molybdenum,platinum, and the like.

While FIG. 2 shows the coupling of the lead body 104 to the paddle body108, it will be appreciated that the lead body 106 is also coupled tothe paddle body 108 in the same manner. Therefore, the discussion withrespect to the construction of the lead body 104 and the coupling of thelead body 104 to the body 108 equally apply to the lead body 106.

FIGS. 3-10 show various examples of paired lead bodies 104, 106. Thelead bodies 104, 106 of these various examples may be constructed invarious manners, such as those discussed above with respect to FIG. 2.Furthermore, in each of these examples, the filars present within thelead bodies 104, 106 may have various configurations, such as beingcoiled as shown above in FIG. 2 or the filars may be linear.

FIG. 3 shows an example of lead bodies 104, 106 connected to a paddle108. The lead body 104 includes a braided conductive shield 302, and alead body 106 that includes a braided conductive shield 304. The braidedshield 302 differs from the braided shield 304 by having differentvalues for at least one physical parameter that results in reducedheating at the electrodes of the paddle 108. In this particular example,there are multiple physical parameters that differ, including the numberof wires and the weave density, which is the percentage of coverage bythe shield material. The weave density difference in this example isprovided by a difference in a pic rate, which is the number of braidwire intersections or pics per unit length of the lead body along agiven axial line. Here, the braided shield 304 has more braid wires anda higher pic rate than the braided shield 302.

In one specific example, the shield 302 is a 100 pics per inch shieldhaving 8 braid wires, 4 in each direction, while the shield 304 is a 200pics per inch shield with 16 braid wires, 8 in each direction. Inanother specific example, the shield 302 is a 75 pics per inch shieldwhile the shield 304 is a 134 pics per inch shield. The particularcombination of pie rates between the two shields 302, 304 may beselected based on the combination of all physical characteristics thatare present within the lead, including such characteristics as theoverall length of the lead bodies 104, 106. Another factor that affectsthe performance of a given combination of physical parameter valuesrelative to lead bodies having identical shields is the frequency of theRF energy being applied. The optimized combination can be found throughempirical studies for a given lead design.

For example, one scenario to consider is a 64 MHz RF field with theelectrodes being located approximately 20 cm from the top of the head ofthe patient, with the center of the MRI coil being 30 cm from the top ofthe head of the patient. With all else being essentially equal betweenthe lead bodies 104, 106 and the shields 302, 304, it has been foundthat a 75/134 pics per inch shield combination produces less heating atthe electrodes than a 100/200 pics per inch shield combination for 50cm, 60 cm, and 100 cm lead lengths. However, it has been found that a100/200 pics per inch shield combination produces less heating at theelectrodes than a 75/134 pics per inch shield combination for 80 cm and90 cm lead lengths.

In other examples where the weave density is different for the braidedshields 302, 304, other physical parameters of the braided shields 302,304 may have the same values or may be different. For instance, bothshields 302, 304 may be constructed of the same material such astantalum wires or may be constructed of different materials such astantalum wires in one shield and titanium wires in the other.

FIG. 4 shows another example of lead bodies 104, 106 connected to apaddle 108. The lead body 104 includes a braided conductive shield 402,and a lead body 106 that includes a braided conductive shield 404. Thebraided shield 402 of this example differs from the braided shield 404by having different values for at least one physical parameter thatresults in reduced heating at the electrodes of the paddle 108. In thisparticular example, the physical parameters that differ include theweave angle, which is the angle formed by the braid wires relative toeither a longitudinal or lateral dimension of the lead body, and theweave density or pic rate.

In other examples, other physical parameters of the braided shields 402,404 may have the same values or may be different. For instance, bothshields 402, 404 may be constructed of the same material such astantalum wires or may be constructed of different materials such astantalum wires in one shield and titanium wires in the other.

FIG. 5 shows another example of lead bodies 104, 106 connected to apaddle 108. The lead body 104 includes a braided conductive shield 502,and a lead body 106 that includes a braided conductive shield 504. Thebraided shield 502 differs from the braided shield 504 by havingdifferent values for at least one physical parameter. In this particularexample, the physical parameters that differ include the braid materialand hence the conductivity of the braid wire. For instance, the shield502 may be constructed of tantalum while the shield 504 may beconstructed of titanium, thereby providing the shields 502, 504 withdifferent values of conductivity.

In other examples where the conductivity differs for the braided shields502, 504, other physical parameters of the braided shields 502, 504 mayhave the same values or may be different. For instance, both shields502, 504 may have the weave density as shown in FIG. 5 or the weavedensity may be different. Likewise, the weave angle may be the same forboth shields 502, 504 as shown in FIG. 5 or may be different. The numberof wires used for each of the shields 502, 504 may be the same or may bedifferent. The diameter of the shields 502, 504 may be the same or maybe different.

FIG. 6 shows another example of lead bodies 104, 106 connected to apaddle 108. The lead body 104 includes a braided conductive shield 602,and a lead body 106 that includes a braided conductive shield 604. Thebraided shield 602 differs from the braided shield 604 by havingdifferent values for at least one physical parameter. In this particularexample, the physical parameters that differ include the number of braidwires that are present where shield 602 has a total of 8 wires with 4 inone direction and 4 in the other. Also, the weave density is lower andin this case the spacing is such that the 4 wires in each direction aregrouped into pairs with spacing between pairs being greater than thespacing between each wire of a pair.

FIG. 7 shows another example of lead bodies 104, 106 connected to apaddle 108. The lead body 104 includes a braided conductive shield 702,and a lead body 106 that includes a braided conductive shield 704. Thebraided shield 702 differs from the braided shield 704 by havingdifferent values for at least one physical parameter. In this particularexample, the physical parameters that differ include the number of braidwires that are present where shield 702 has a total of 8 wires with 4 inone direction and 4 in the other. Also, the weave angle relative to thelateral axis is lower.

FIG. 8 shows another example of lead bodies 104, 106 connected to apaddle 108. The lead body 104 includes a braided conductive shield 802,and a lead body 106 that includes a braided conductive shield 804. Thebraided shield 802 differs from the braided shield 804 by havingdifferent values for at least one physical parameter. In this particularexample, the physical parameters that differ include the number of braidwires that are present where shield 802 has a total of 12 wires with 8in one direction and 4 in the other. As shown, the spacing between eachturn of the group of 4 wires is by a greater amount than the spacingbetween each wire of the group.

FIG. 9 shows another example of lead bodies 104, 106 connected to apaddle 108. The lead body 104 includes a braided conductive shield 902,and a lead body 106 that includes a braided conductive shield 904. Thebraided shield 902 differs from the braided shield 904 by havingdifferent values for at least one physical parameter. In this particularexample, the physical parameters that differ include the number of braidwires that are present where shield 902 has a total of 8 wires with 4 inone direction and 4 in the other. Also, the weave density is lower andin this case the spacing between pairs is greater than the spacingbetween each wire of a pair.

FIG. 10 shows another example of lead bodies 104, 106 connected to apaddle 108. The lead body 104 includes a braided conductive shield 1002,and a lead body 106 that includes a braided conductive shield 1004. Thebraided shield 1002 differs from the braided shield 1004 by havingdifferent values for at least one physical parameter. In this particularexample, the physical parameters that differ include diameter of theshield 1002 with a lower weave angle relative to the axial dimension.Also, the weave density is lower and in this case the spacing is unevenby having the 4 wires in each direction grouped into pairs with spacingbetween pairs being greater than the spacing, between the each wire of apair.

While embodiments have been particularly shown and described, it will beunderstood by those skilled in the art that various other changes in theform and details may be made therein without departing from the spiritand scope of the invention.

What is claimed is:
 1. A medical lead, comprising: a first lead bodyhousing a first filar connected to a first proximal contact on the firstlead body, the first lead body having a first conductive shield; asecond lead body housing a second filar connected to a second proximalcontact on the second lead body, the second lead body having a secondconductive shield, the second lead body being adjacent to the first leadbody so that destructive interference of at least some radio frequenciesoccurs on the first filar and the second filar; and a body housing aplurality of electrodes, the body being coupled to the distal end of thefirst and second lead bodies with a first electrode of the pluralityconnected to the first filar and a second electrode of the pluralityconnected to the second filar.
 2. The medical lead of claim 1, whereinat least one physical parameter of the first conductive shield is thesame for the second conductive shield.
 3. The medical lead of claim 2,wherein the first conductive shield and the second conductive shieldcomprise braided wires.
 4. The medical lead of claim 3, wherein the atleast one physical parameter comprises at least one of weave density,weave angle, shield diameter, braid wire conductivity, and number ofbraid wires.
 5. The medical lead of claim 2, wherein the first andsecond conductive shields comprise tantalum.
 6. The medical lead ofclaim 1, wherein the first conductive shield is embedded within thefirst lead body and the second conductive shield is embedded within thesecond lead body.
 7. A medical system, comprising: a first lead bodyhousing a first filar connected to a first proximal contact on the firstlead body, the first lead body having a first conductive shield, thefirst lead body having a first electrode connected to the first filar;and a second lead body housing a second filar connected to a secondproximal contact on the second lead body, the second lead body having asecond conductive shield, the second lead body having a second electrodeconnected to the second filar, the second lead body being positionedadjacently to the first lead body so that destructive interference of atleast some radio frequencies occurs on the first filar and the secondfilar.
 8. The medical system of claim 7, further comprising a bodyhousing the first and second electrodes, and wherein the distal ends ofthe first and second lead bodies are coupled to the body.
 9. The medicalsystem of claim 7, further comprising a stimulation device and whereinthe first lead body and the second lead body are coupled to thestimulation device.
 10. The medical system of claim 7, wherein at leastone physical parameter of the first conductive shield is the same forthe second conductive shield.
 11. The medical system of claim 10,wherein the first conductive shield and the second conductive shieldcomprise braided wires.
 12. The medical system of claim 11, wherein theat least one physical parameter comprises at least one of weave density,weave angle, shield diameter, braid wire conductivity, and number ofbraid wires.
 13. The medical system of claim 10, wherein the first andsecond conductive shields comprise tantalum.
 14. The medical systemclaim 7, wherein the first conductive shield is embedded within thefirst lead body and the second conductive shield is embedded within thesecond lead body.
 15. A method of implanting a medical system,comprising: providing a first lead body housing a first filar connectedto a first proximal contact on the first lead body, the first lead bodyhaving a first conductive shield, the first lead body having a firstelectrode connected to the first filar; providing a second lead bodyhousing a second filar connected to a second proximal contact on thesecond lead body, the second lead body having a second conductiveshield, the second lead body having a second electrode connected to thesecond filar; and implanting the first lead body and the second leadbody such that the second lead body is positioned immediately adjacentto the first lead body so that destructive interference of at least someradio frequencies occurs on the first filar and the second filar. 16.The method of claim 15, wherein a body houses the first and secondelectrodes, and wherein the distal ends of the first and second leadbodies are coupled to the body.
 17. The method of claim 15, furthercomprising coupling the proximal ends of the first and second leadbodies to a stimulation device.
 18. The method of claim 15, wherein atleast one physical parameter of the first conductive shield is the samefor the second conductive shield.
 19. The method of claim 18, whereinthe first conductive shield and the second conductive shield comprisebraided wires.
 20. The method of claim 19, wherein the at least onephysical parameter comprises at least one of weave density, weave angle,shield diameter, braid wire conductivity, and number of braid wires.